Have you ever been annoyed to find that your Mac won’t go to sleep when you tell it to? US Macworld reader wjv found that, in Mac OS X 10.6 and later, there’s a simple way of finding out what’s keeping your Mac awake. To do so, run the following command in your Terminal: pmset -g assertions .
In the first section of output, you’ll see the status of two kernel assertions (essentially, assumptions the system makes about the state of your system) named PreventSystemSleep and PreventUserIdleSystemSleep. An accompanying status of 1for either of these means that it is currently triggered. For example, here’s what I see when I run that command on my Mac mini:
Assertion status system-wide:
PreventUserIdleDisplaySleep 0
PreventSystemSleep 0
PreventUserIdleSystemSleep 1
ExternalMedia 1
DisableLowPowerBatteryWarnings 0
UserIsActive 0
ApplePushServiceTask 0
BackgroundTask 0
Below that, you’ll see something like this:
Listed by owning process: pid 9165(iTunes): [0x0000000100001192] 00:18:23PreventUserIdleSystemSleepnamed:
"Nameless (via IOPMAssertionCreate)"
pid 175(coreaudiod): [0x0000000100001287] 00:12:39 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,2:0'.noidlesleep"
